class Championship:
    __name__ = 'championship'
    classification = fields.One2Man('classification', 'championship', 'Classification',
    context={
       'by_championsihp': True,
    })

class Classification:
   ___name__ = 'classification'

   def table_query(cls):
        #Compute the classification
        if Transaction().context.get('by_championship'):
             # Group by championship
        else:
             # Championship is None